<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .outer {
            border: 10px red solid;
            /* float: left; */
            /* display: inline-block; */
            overflow: hidden;
        }
        .inner {
            width: 100px;
            height: 100px;
            background-color: #dfa;
            float:left;
        }
    </style>
</head>
<body>
    <div class="outer">
        <div class="inner"></div>
    </div>

    <div style="width: 100px;height: 100px;background-color: yellow;"></div>
</body>
</html>